Learning of object-object associations by monkeys

Monkeys were trained in tasks where stimulus objects were presented in pairs, one object of a pair concealing the other, and the monkeys had to displace the top object followed by the bottom object in order to obtain a food reward. In two experiments it was demonstrated that under these conditions the animals formed object-object associations such that the top object recalled in memory the bottom object that had previously been found underneath it. The monkeys were able to discriminate in recall between bottom objects that were identical in secondary reinforcing value and differed only in colour.